A transparent aluminum oxide ceramic is used, for example, in high-pressure gas discharge lamps, as described, for example, in EP-A-0 327 049 and DE-A-23 07 191. A metallic conductor has to be guided into the aluminum oxide ceramic, which is generally tubular and provided as a discharge vessel, and has to be connected to the aluminum oxide ceramic in a vacuum-tight manner. For this purpose, there is provision for a metallization paste to be sintered onto the aluminum oxide ceramic, so that a metal layer is obtained. The metallic conductor is then sealed to the metal layer in a vacuum-tight manner, for example by means of a brazing solder. U.S. Pat. No. 3,590,468 has described a process for forming a seal between a pure aluminum oxide and a metal. Therefore, the prior art has only disclosed a material composite comprising an aluminum oxide ceramic and a metal, but not a material composite comprising an aluminum oxide sapphire and an aluminum oxide ceramic.